What is Reverberation? Definition from NCERT Class 9 Science

Sound is an interesting phenomenon. It has various aspects, and all of them make one ponder upon them for some time. For instance, there is a difference in the sound of a movie when you watch it in a theatre and when you watch it at home on your desktop or TV.

The difference in the sound is not just because of the volume levels but also because of the time for which the sound prevails.

You can notice the same persistence of sound when attending an assembly in a closed auditorium or enjoying a musical concert in an enclosed hall. All these examples are applications of one of the interesting facts about sound ‘Reverberation’. This article describes the definition of reverberation from NCERT class 9 Science. 

What is the sound?

A form of mechanical energy that propagates as a wave in the form of compressions and rarefactions in the medium is known as sound. These waves are produced through the vibration of objects and create the sensation of hearing.

You can check out the NCERT Solutions for Class 9 Science Chapter 12 Sound. 

What is an echo?

The echo is simply a reflection of the sound wave. When a sound wave collides with a hard surface such as a wall, mountain, or fence, the wave gets reflected. The reflected wave arrives at a listener with a delay. The delay in the wave is directly proportional to the distance of the reflecting surface from the source of the sound and the listener.

When there are multiple surfaces from which the sound wave can get reflected at suitable distances, it gets reflected multiple times, resulting in multiple reflections. 

Reverberation

When there are multiple surfaces with suitable distances for sound to collide with, multiple reflections of sound occur. Since the wavelength of sound is much longer than that of light, repeated reflection results in the persistence of sound even after the source have stopped, called reverberation. The NCERT class 9 Science definition of reverberation states the following: The persistence of sound caused by the multiple sound reflections even after the source has stopped is called reverberation. 

When the time period between original and reflected sound is less than 0.1 sec, reverberation occurs. Since the reflected sound stays longer than the original sound, the original sound cannot be distinguished from the reflected sound. When the sound gets reflected by several sources, the reflections pile up and start reducing gradually as the sound gets absorbed by the surfaces.

To clearly understand the chapter ‘Sound’ of the NCERT class 9, students should make sure they study the important concepts.

Difference between echo and reverberation

Echo and reverberation are often confused with being one. However, there is some difference between the two.

Reverberation occurs due to the multiple reflections of a sound wave resulting in the persistence of the sound even after the source sound has stopped. A human brain cannot distinguish between the original and reflected sounds due to the short time difference between the two sounds received by the ear. The brain thus perceives it as one continuous sound.

Whereas echo is just a pulse of sound heard twice. A delay of about 50ms or more between the original and reflected sounds falling on the ear helps the human brain distinguish between the two waves.

Advantages of Reverberation

Reverberation is a phenomenon related to the multiple reflections of the sound wave. When in an auditorium, the overlapping of sound waves makes a difference in the effect of sound. 

In an orchestra hall or theatre, reverberations enhance the quality of sound manifold. It makes the music pleasant and with the right amount of reverberation employed. Sound engineers are employed while constructing these halls to ensure the optimum effect of reverberation.

Disadvantages of Reverberation

Suppose reverberation of sound takes place in a normal room without any proper design or sound-absorbing surfaces. In that case, the sound reflections become repetitive, and the sound does not disappear for a long period. 

In this case, the listener happens to listen to both the original sound and the reflected sound. And if there is enormous reverberation, the sound results in chaos giving rise to unpleasant sounds.

Applications of Reverberation

Reverberation is employed in various music-related areas. The music or speech in a space with a sound reflective surface creates reverberation naturally.

It is used artificially to stimulate reverb through certain means, including a chamber reverberator, a plate reverberator, a spring reverberator, and a digital reverberator. Plate reverberators are designed using metal plates to vibrate and can be used as an alternative to speakers. The concept of a reverberator is useful in a wide range of aspects.

Following are certain applications of multiple reflections of sound:

• Many musical instruments are designed to have a tube followed by a conical opening that reflects the sound waves repeatedly without the sound waves getting scattered and making the wave travel in a particular direction.

The successive reflections of sound add up to increase the amplitude of the sound.

• Stethoscope used by doctors also works on the principle of successive reflection of sound, which is carried through the stethoscope tube.
• The ceilings of auditoriums or theatres are constructed to be curved so that the reflected sound reaches all corners of the hall.

How do we reduce excess?

When there are no proper arrangements in a room to handle reverberation, it results in chaos. In short intervals, the overlapping of sound waves causes indistinct sounds, making it impossible to understand what is being spoken in the room. The sound becomes distorted and blurred.

Excessive reverberation must be thus removed for the sound to make it audible. Excessive reverberation can be removed by certain things as follows:

• Modern auditoriums or concert halls are designed to have optimum reverberation. 
• Heavy curtains are used on the doors and windows of the hall.
• Carpets are laid on the floor to absorb sound. 
• The ceiling and walls are covered by sound-absorbent materials like compressed fire boards and rough plasters.
• Seats in these halls are made of sound material.
• The walls are covered with soundproofing panels to absorb sound.
• Examples of sound-absorbent materials are porous materials like mineral wool and fiberglass. The sound energy gets converted to heat through friction when the sound wave penetrates mineral wool.

Conclusion

The chapter ‘Sound’ from the NCERT class 9 discusses various important concepts related to sound waves, their generation, propagation, and properties. 

Reverberation is the phenomenon that occurs when the sound gets reflected multiple times from obstacles at suitable distances within a time period of less than 0.1 sec. It causes overlapping waves without letting the human brain distinguish between the original and reflected sound. It makes the brain perceive the sound as one continuous sound. 

Reverberation is thus the persistence of sound even after the source has stopped due to the multiple reflections of sound. 

When within optimum limits, reverberation is desirable in auditoriums or enclosed halls with proper sound-absorbent design. However, excessive reverberation may make the sound blurry and irritating. It is thus important to reduce reverberations whenever required.

FAQs

1. What is the reverberation of sound, and how to reduce it?

The persistence of sound caused by the multiple reflections of sound even after the source has stopped is called reverberation. This happens when the time period of reflection of the sound is less than 0.1s. For multiple reflections of sound, the obstacles present in a room for sound reflections must be at suitable distances.

Reverberation may cause chaos when it is not within the optimum limits. In such cases, it becomes necessary to reduce reverberations. It can be done by using proper sound-absorbent materials in the enclosed halls. Use of sound-absorbing curtains and carpets should be done. The ceilings and walls should be sound-absorbing materials like compressed fire boards or rough plasters.

2. Why are the ceilings of concert halls curved?

Reverberation plays an important role in enhancing sound quality in concert halls or auditoriums. To ensure the proper usage of regeneration, these halls are designed using the proper technology and material. Therefore, sound engineers are employed for constructing these halls. The concert halls’ ceilings are curved so that the sound waves colliding on the ceiling are reflected equally in all the corners of the hall. Concert halls being large, the sound might not reach every corner of the hall. The curved ceilings act as a soundboard that reflects the sound to the audience.

3. What are the applications of reverberation of sound?

Reverberation is nothing but multiple reflections of sound that happen within a very short period. It results in the persistence of sound even after the source of sound has stopped.

Reverberation plays an important role in concert halls, auditoriums, or orchestra halls. Reverberation in these halls improves sound quality, drastically offering a pleasant experience to the audience.

Certain means using artificial stimulation of reverbs are created like reverb chambers, spring reverberated, plate reverberated, and digital reverberators. 

4. What is the difference between echo and reverberation?

Echo is created when a sound wave reflects from a hard surface. The echo can be easily distinguished from the original sound as the time required for reflection is more than 50ms. Also, the distance for an echo to be created is more.

Whereas reverberation is caused when the sound is reflected multiple times within a closed area leading to its persistence even when the source has stopped. For reverberation to happen, the time period of reflection is less than 0.1s.

5. What will happen if the reverberation time is too long?

Reverberation is a phenomenon that occurs when the light gets reflected in an enclosed hall with multiple obstacles present for the sound wave to get absorbed. Reverberation occurs when the obstacles are at suitable distances and the time of reflection is less than 0.1s.

However, if reverberation takes place in a long hall and the reverberation time is too long, the reflected sound waves will not overlap, and there will not be the persistence of sound. The effect of the reflections of sound would be nothing but an echo.

6. How do I prepare for the chapter Sound to score well?

For the NCERT class 9 Science, Sound is an important chapter. Students can score well in their exams if they study well for this chapter.

The chapter has many interesting concepts related to sound waves, their generation, propagation and characteristics. To prepare well for this chapter, students must be well aware of the important concepts of this chapter. 

To get an idea of the questions that can be asked in the exams, students must solve the sample question papers. It will help them get an idea of the important questions and also make them revise concepts. Studying the NCERT solutions for class 9 will also be useful as it will help the students get answers to the questions present in the book. Other sources to go through NCERT solutions for class 9 are:

RD Sharma Solutions

RS Aggarwal Solutions

Lakhmir Singh Solutions